The present invention relates to a primer composition effective in bonding an addition reaction type hydrocarbon polymer securely to various substrates. More particularly, the invention relates to a primer technology for achieving improved bonds to substrates and a technology of improving the adhesion of an addition type cured product which comprises coating a primer on a substrate and then applying an addition reaction type curable composition comprising a hydrocarbon polymer thereon and letting it cure in situ.
A curable resin (also known as an addition type curable composition) in which a hydrocarbon polymer containing at least one alkenyl group within its molecule is crosslinked with a curing agent having two or more silicon-bound hydrogen atoms per molecule has been disclosed in Japanese Kokai Publication Hei-2-75644 and Japanese Kokai Publication Hei-3-181565, for instance. The cured product derived from such a composition (which artifact is also known as an addition type cured product) has excellent weather resistance, high heat resistance and low moisture permeability and, therefore, is expected to find application in a broad spectrum of end uses.
Particularly when an addition type curable composition comprising a hydrocarbon polymer is used as a coating or dipping agent or a sealant for various substrates, it must have a high adhesiveness for the various substrates. The known technology of imparting adhesiveness to such an addition type curable composition comprising a hydrocarbon polymer involves addition of various adhesion-improving agents to an addition type curable composition. By way of illustration, Japanese Kokai Publication Hei-4-185687 discloses a technique comprising adding a silane coupling agent to an addition type curable composition; Japanese Kokai Publication Hei-08-134165 discloses a technique comprising adding a nitrogen-containing epoxy compound and a silane coupling agent; Japanese Kokai Publication Hei-08-134165 discloses a technique comprising adding an isocyanate-containing compound and a silane coupling agent; Japanese Kokai Publication Hei-09-316293 and Japanese Kokai Publication Hei-10-204222 disclose a technology comprising adding a silane coupling agent, an alkoxysilane condensate and an organoaluminum and/or organotitanium compound. These techniques have the disadvantage, inter alia, that, depending on the kind of silane coupling agent, a retardation of cure may take place.
The object of the invention is to provide a primer composition which is effective in achieving a firm bond between a various substrate and a cured product derived from a hydrosilylation-curable composition comprising a hydrocarbon polymer containing at least one alkenyl group per molecule and a curing agent having two or more hydrogen atoms bound to silicon per molecule and to provide a bonding method.
Landing on a concept representing a complete departure from he prior art, the inventors of the present invention discovered that an addition type curable composition comprising a hydrocarbon polymer containing at least one alkenyl group per molecule and a curing agent having two or more hydrogen atoms bound to silicon per molecule and a cured product derived therefrom can be bonded to various substrates by utilizing a primer composition.
The present invention, therefore, is concerned with a primer composition comprising the following (A), (B), (C) and (D) components:
(A) a hydrocarbon polymer containing at least one alkenyl group per molecule
(B) a silane coupling agent
(C) a polyvalent alkoxysilane and/or a condensation product thereof, and
(D) an organoaluminum compound and/or an organotitanium compound.
The present invention is further concerned with a primer composition comprising the following (E) component in addition to said (B), (C) and (D) components:
(E) a vinyl copolymer having a backbone structure substantially comprised of a vinyl copolymer chain and containing a silicon-containing group having a hydroxyl or hydrolyzable group bound to a silicon atom and capable of crosslinking by siloxane bonding terminally of its backbone and/or side chain.
In this invention, the preferred (E) component vinyl copolymer has a number average molecular weight in the range of 500 to 50000 and contains a hydrolyzable silyl group of the general formula (1) terminally of its backbone and/or side chain. 
in which R1 and R2each independently represents an alkyl group of 1 to 20 carbon atoms, an aryl group of 6 to 20 carbon atoms, an aralkyl group of 7 to 20 carbon atoms, or a triorganosiloxy group of the formula (Rxe2x80x2)3SiOxe2x80x94, where Rxe2x80x2 groups each independently represents a substituted or unsubstituted hydrocarbon group containing 1 to 20 carbon atoms; X groups each independently represents a hydroxyl group or a hydrolyzable group; a denotes 0, 1, 2 or 3; b denotes 0, 1 or 2; but both a and b are not equal to 0; m denotes an integer of 0 to 19.
A further preferred composition comprises a hydrocarbon polymer containing at least one alkenyl group per molecule, that is said (A) component, in addition to said (B) to (E) components.
More preferably, in this invention, the (A) component hydrocarbon polymer is a polyisobutylene polymer having a number average molecular weight in the range of 500 to 50000 and containing at least one alkenyl group terminally of its backbone and/or side chain.
Moreover, in this invention, the (B) component silane coupling agent is a silane coupling agent having at least one of epoxy group, a vinyl group and a (meth)acryloyl group, and may advantageously be a mixture of two or more specific silane coupling agents.
In addition, a further preferred primer composition of the invention comprises a hydrosilylation catalyst as (F) component.
The present invention is further directed to a bonding method for bonding a cured product to a substrate
which comprises coating a primer composition comprising a silane coupling agent as said (B) component on a substrate
and then applying a curable composition comprising a hydrocarbon polymer having at least one alkenyl group per molecule onto the primed substrate.
In this invention, it is preferable to formulate a polyvalent alkoxysilane and/or a condensation product thereof as (C) component and an organoaluminum compound and/or an organotitanium compound as (D) component in addition to said (B) component. Furthermore, it is preferable to add a hydrosilylation catalyst as (F) component and still more preferably add an organic solvent as (G) component.
The invention is further concerned with a bonding method for bonding a cured product to a substrate
which comprises coating a primer composition comprising a polyvalent alkoxysilane and/or a condensation product thereof as (C) component and an organoaluminum compound and/or an organotitanium compound as (D) component on a substrate
and then applying a curable composition comprising a hydrocarbon polymer having at least one alkenyl group per molecule to the primed substrate.
Preferably, in this invention, said hydrocarbon polymer having at least one alkenyl group per molecule is a polyisobutylene polymer containing at least one alkenyl group terminally of its backbone and/or side chain and having a number average molecular weight in the range of 500 to 50000.
Furthermore, in this invention, the (B) component silane coupling agent is one or more kinds of silane coupling agent(s) containing an epoxy group, a vinyl group or a (meth)acryloyl group.
The invention is further concerned with a laminate comprising a substrate and a cured product as obtainable by the above bonding method.